1. Field of the Invention
The present invention is directed toward apparatus, systems and methods for use in three-dimensional printing.
2. Description of the Related Art
Three-dimensional printing is a process of depositing successive layers of powder onto a substrate, and causing portions of each layer to adhere or bind to themselves and to adjacent earlier-deposited layers through the action of a liquid called a binder. Through this sequential process a three-dimensional product is ultimately formed. Because of the sequential nature of this process, products having complex shapes and even interlocking parts can be formed, products that are otherwise extremely difficult if not impossible to fabricate through traditional means.
Powder has typically been deposited through one of two methods. One method has been to spread dry powder with a roller across the top of the substrate or prior layer. This method is suited to creating powder layers with thicknesses of around 0.005 inch (127 microns) or greater, and to powders whose average particle size is greater than a minimum value which is somewhere in the range of 5 to 20 microns.
The other method of depositing powder has been to deposit layers of a powder-carrying slurry onto the substrate or prior layer. The slurry comprises a carrier liquid with a fairly high content of suspended solid particles. The slurry carrier liquid may be formulated to encourage the particles to remain suspended and to discourage them from agglomerating with each other. A discharge of slurry (usually continuous) from a nozzle is rastered across the bed. Slurry deposition has typically been used for depositing rather thin layers of powder whose particle size is finer than is practical with roller-spreading of powder. When the slurry has been deposited, all or most of the slurry carrier liquid must be removed from the deposited layer before printing of binder liquid. This has been accomplished through some combination of percolation, natural evaporation and evaporation due to externally applied heat.
After each layer of powder has been deposited on the build bed, by either the roller method or the slurry method discussed above, a printhead dispenses binder or another fluid onto preselected areas of the powder to form a layer of the final product. The binding action can be achieved through dissolution of powder by the binder followed by resolidification when the binder evaporates, or through an adhesive which is initially dissolved in or mixed with the binder and is left behind on the powder when the volatile component(s) of the binder evaporate. Typically the binder is selected to have an appropriate degree of volatility so that its volatile component(s) evaporate, leaving behind solidified powder, after a desired amount of time.
The printhead can operate in a raster mode, which is similar to an inkjet printer, progressively making rapid, lateral passes across the build bed, moving slightly forward with each pass, until it has dispensed fluid along the entire length of the build bed. The lateral direction of the printhead has been referred to as the fast axis, as the printhead moves along this axis relatively quickly. The longitudinal direction, perpendicular to the fast axis, has been referred to as the slow axis, because movement along the slow axis does not occur during fast axis movement and in general is slower. It has also been possible to perform vector printing, in which there is simultaneous motion in both horizontal axes to enable the printhead to move in curved paths. It has also been possible to use both raster printing and vector printing in a print job.
Controlling the duration of drying and the extent of drying before application of the next layer of powder has been important because these influence bleeding (i.e., the spreading of dispensed liquid in the powder before it dries, which affects dimensions and the surface finish of a part) and because they affect the adhesion between layers (i.e., the strength of the printed part).
Analyzing both the rate and the extent of drying between successive layers has indicated that there is an optimal range for each of these parameters. The evaporation rate of a given binder at the operating temperature, which is typically room temperature, may or may not be within that optimal range. Presently, one design variable available to influence drying rate is the formulation of the binder. Another available variable is the temperature of the print bed, which impacts the entire machine design and process. Yet another variable is the length of time between depositing layers, which affects the extent of drying between layers but does not affect the rate of drying and hence does not control bleeding.
Heating during portions of the three-dimensional printing process is known in crude forms. For example, externally applied heat has been used for purposes of evaporating slurry carrier liquid. However, this external application of heat to a slurry-deposited layer, which has typically occurred prior to printing of binder onto that layer, has caused evaporation of slurry carrier liquid. This is not the same as causing the evaporation of binder liquid, which occurs after printing of binder onto that layer.
Heating of the build bed to accelerate evaporation of the volatile part of the binder liquid has been proposed, such as in U.S. Pat. No. 5,204,055, but using fixed-place heat sources located sufficiently far away from the build bed to allow room for all the other equipment is not very precise in the application of heat directly to the bed, or in uniformity of delivery of heat to all places of the bed, and in such a manner as to achieve a desired remaining saturation of the printed portions of the layer after completion of the interlayer drying. For example, in construction of parts by three-dimensional printing, some layers may have large areas printed upon by binder liquid while another layer may have only small areas printed upon by binder liquid. Treating all of these layers the same as far as application of interlayer drying heat produces results which differ between these situations as far as what is the saturation of the bed at the time of the spreading of the next layer of powder and subsequent printing upon it.
Existing three-dimensional printing machines have not been sufficiently cleanable to be useful for medical manufacturing purposes. Likewise, refilling, replacing and/or changing the powder in existing three-dimensional printing machine has been a difficult job and could spread powder throughout the machine, requiring additional cleaning and, possibly, disinfecting. Much of the process of loading and unloading powder as well as cleaning has involved the entire machine, making the entire machine unavailable for any other purpose during that time.
For some purposes it may be desirable to use binder liquids, which comprise organic solvents. Such solvents may be particularly desirable for use in certain medical applications, which may require dissolution of substances not soluble in water-based liquids. Organic solvents may have hazards not found with water-based liquids. For example, chloroform, an important organic solvent for purposes of medical interest, is a suspected human carcinogen. Many other organic solvents of interest, such as ethanol and other alcohols, and acetone, in addition to being in some cases toxic, are flammable. Flammable substances can be explosion hazards for certain concentrations of their vapors in air or certain vapor/oxygen ratios. Existing three-dimensional printing machines intended for more ordinary binders, usually aqueous binders, have not had features appropriate to adequately deal with these hazards.
Existing three-dimensional printing machines may have had an enclosure designed to prevent objects or operators' body parts from accidentally entering into the workspace. However, they have not had an enclosure sufficient to maintain an environment suitable for processing medical and pharmaceutical products and devices.
Existing three-dimensional printing machines may have heat loads without having good ways of managing and removing that heat. It can be important to maintain well-controlled temperature of components near the working region, because for example the dispensing of binder liquid can suffer from irregularities if there are significant variations in the temperature of the liquid as it is dispensed.
Existing three-dimensional printing machines typically have allowed manual changeover from one powder to another and associated cleaning procedures, but not in a quick or easy manner.
Precision in determining dispensed fluid volume has traditionally not been critical. Existing three-dimensional printing machines have dispensed binder at flowrates which are known to an accuracy suitable for industrial purposes, but not to an accuracy suitable for demanding manufacturing such as manufacturing of medical articles. Furthermore, in existing three-dimensional printing machines there has been no way of measuring the actual delivered flowrate during printing or even verifying the delivery of a drop at any given location where delivery of a drop was commanded.
Thus, prior to the present invention there existed a need for more precise and controlled delivery of heat to achieve interlayer drying; isolation of the working region from the outside for reasons of cleanliness and in connection with the vapors of organic solvents; better control of the temperature of the working region; better accuracy in the flowrates of binder fluid dispensed; matching of delivered flowrate for multiple dispensers; verification of delivered flowrate or drops; provision for easier changeover of the machine from one powder to another; cleanability; and other needs.